Haemodynamic responses in chronically painful, human trapezius muscle to cold pressor stimulation

The aim was to compare haemodynamic responses in trapezius muscles to cold pressor stimulation in individuals with localized trapezius myalgia and asymptomatic controls. Nine males with chronic localized pain in the trapezius (mean age, 23.2 years) and nine male controls (mean age, 24.6 years) who had no medical history of migraine, hypertension or sustained pain in the trapezius region were investigated. Two experimental (cold pressor and mock) trials were performed in a randomly assigned sequence. In the cold pressor trial the participant's left foot and ankle were immersed in 4 degrees C cold water for 2 min; the mock trial was done without that stimulus. Blood volume was continuously recorded 1 min before, 2 min during, and 5 min after cold pressor stimulation using near-infrared spectroscopy. Each participant's blood-volume data were baseline-corrected and submitted to statistical analysis. Results showed that the individuals with muscle pain exhibited a significantly lower mean blood volume than the controls during cold pressor stimulation (p = 0.0367). Upon withdrawal of that stimulation, the mean blood volume in both groups fell below the baseline. These results suggest that individuals with chronic regional trapezius myalgia have less capacity to vasodilate this muscle during cold pressor stimulation than those without such myalgia. It is not yet known if this difference in the haemodynamic response is a cause or an effect of the myalgia.